1. Technical Field
The present invention generally relates to an electro-optical device, an illumination device, an electronic apparatus, and a method for production of the electro-optical device. More particularly, the invention relates to an electro-optical device, an illumination device, an electronic apparatus, and a method for production of the electro-optical device, which is provided with a flexible printed circuit board on which light sources are mounted.
2. Related Art
A known example of electro-optical devices for displaying images is a liquid crystal device. A liquid crystal device modulates light that passes through a liquid crystal material provided at a plurality of pixels thereof so as to display images such as pictures and characters. Having an opposing pair of substrates that have respective electrodes formed thereon, such a liquid crystal display device performs light modulation to display images by turning voltages applied to the plurality of pixels thereof ON/OFF in a selective manner, where the intersection areas of the respective electrodes are defined as the plurality of pixels.
In such a liquid crystal device, an illumination device is used as means for performing transmissive-mode display. In order to realize a flat and compact body of the liquid crystal device, the illumination device has a configuration in which light sources such as LEDs are mounted at the edge of an optical waveguide board on a flexible printed circuit board (FPC) so as to guide light that is emitted from the light source toward a liquid crystal panel.
In the illumination device having such a configuration, in order to guide light coming from the light source toward the liquid crystal panel with a satisfactory light-guiding performance, it is necessary to ensure that the optical axis of the light source is never shifted with respect to the optical waveguide board so that the light emitted from the light source enters efficiently into the optical waveguide board.
For the purpose of meeting the above optical requirements, JP-A-2005-17613 (in particular, refer to the scope of claims and FIG. 1 thereof) proposes an electro-optical device having a configuration in which an optical waveguide board and light sources are fixed so that the optical axis of the light source is never shifted with respect to the optical waveguide board so that an ample amount of light enters the optical waveguide board, which is provided for guiding light from the light source to the liquid crystal panel. More specifically, as illustrated in FIG. 16, the above-identified patent document discloses an electro-optical device 300 that includes an electro-optical panel, an optical waveguide board 303, a guide unit 305 that supports the electro-optical panel and the optical waveguide board 303, and a flexible printed circuit board 309 on which light sources 307 are mounted. According to the electro-optical device 300 described in the above-identified patent document, a double-faced adhesive tape 310 that sticks the flexible printed circuit board 309 and the optical waveguide board 303 together is adhered on the optical waveguide board 303. The double-faced adhesive tape 310, which is formed roughly in the shape of letter “U”, or in other words, the shape of one half of square brackets, and is made up of one first line portion 311 and two second line portions 312 which are perpendicular to the first line portion 311, is adhered thereon in such a manner that it surrounds light input portions 3031 of the optical waveguide board 303.
According to the electro-optical device 300 described in the above-identified patent document, JP-A-2005-17613, the flexible printed circuit board 309 does not contact the optical waveguide board 303 directly due to the presence of the adhesive member (i.e., adhesive tape) 310. For this reason, light that was emitted from the light source 307 occasionally leaks out through a gap where the adhesive member 310 is not present, which could result in lower light utilization efficiency and/or unstable brightness. In addition to the above disadvantages, as illustrated in FIG. 17, the entire thickness of the electro-optical device 300 as a whole is increased by a thickness of the adhesive member 310, which is denoted as T. Moreover, the optical axis S of light emitted from the light source 307 is shifted disadvantageously.
As a conventional solution to overcome the above disadvantages, FIG. 18 illustrates an alternative fixing method according to which the flexible printed circuit board 309 is fixed only to a chassis (i.e., casing) 153 by an adhesive member 353, meaning that the flexible printed circuit board 309 is not fixed to the optical waveguide board 303 at all. Disadvantageously, according to such an alternative fixing method, however, the positional relationship between the light sources 307 and the optical waveguide board 303 is not maintained as these get shifted with respect to each other because the flexible printed circuit board 309 is not fixed to the optical waveguide board 303, which makes it impossible to obtain stable brightness.